The invention relates to a process for the complete or partial combustion of carbon-containing fuel with an oxygen containing gas in a reactor in which the gas formed is removed at the top of the reactor and slag at the bottom of the reactor. The invention also relates to a reactor for use in said process.
The combustion may be complete or partial, the object of the combustion process being in the first case the production of heat, for example, for direct or indirect power generation and in the second case, the production of synthesis gas mainly consisting of carbon monoxide and hydrogen.
By the term carbon-containing fuel is generally meant coal or another solid fuel, such as brown coal, peat, wood etc., but also liquid fuels, such as tar sand oil or shale oil can be used.
The reactor in which combustion takes place may have various shapes, such as the shape of a sphere, cone or cylinder. In order to meet the high strength requirements demanded of the reactor on the one hand and to keep the costs of manufacture within reasonable limits on the other hand, the reactor preferably has the shape of a circular cylinder.
The supply of the carbon-containing fuel and the oxygen-containing gas can take place through the bottom of the reactor. It is also possible to supply one of the reactants through the bottom of the reactor and one or more others through the side wall of the reactor. However, both the fuel and the oxygen-containing gas and a temperature moderator, if any, are preferably supplied through the side wall of the reactor. This is advantageously performed by means of at least two burners arranged symmetrically in relation to the longitudinal axis of the reactor in a lower part of the side wall.
Since carbon-containing fuel is usually of mineral origin, it invariably also contains, in addition to carbon and hydrogen, a certain quantity of inorganic, uncombustible material often referred to by the term ash which is separated during the complete or partial combustion of mineral fuel. Depending on the operating conditions under which combustion takes place, in particular the temperature and the quality of the fuel, the ash is mainly obtained in solid or liquid condition or in a combination thereof. The larger part of the liquid ash obtained, further referred to as slag, flows along the reactor wall and is generally collected in a waterbath located below the reaction zone of the reactor, where the slag cools and solidifies. Subsequently, the solidified slag can be discharged as a slurry in a relatively simple manner.
The waterbath generally forms an integral part of the reactor and is located directly below the reaction zone proper where the combustion process takes place. Because a usually substantially elevated pressure prevails in the reactor, a lock system is used to discharge the slurry of solidified slag from the reactor. In the reactor the reaction zone is normally separated from the cooling zone with the waterbath by a partition wall having a centrally located discharge opening for the slag. The slag discharge opening, often referred to by the term slagtap, should be rather narrow for various reasons. In the first place, the escape of unconverted coal through the discharge opening should be avoided as much as possible. Secondly, the slag discharge opening should be rather narrow in order to prevent that water vapor formed during the cooling of the slag in the waterbath from entering the reaction zone in excessive quantities. The penetration of the water vapor into the reaction zone proper should be limited, since the water vapor could unfavorably affect the combustion process when it enters the reaction zone in substantial quantities. Moreover, the water vapor will have a solidifying effect on the slag in the reaction zone, with the result that the slag flow to the slag discharge opening will be reduced.
Depending on the conditions in the reaction zone and the type of carbon-containing fuel used the slag will more or less easily flow to the slagtap and subsequently enter the cooling zone. If the slag flow through the slagtap is reduced it may give rise to blockage of the slagtap. If the slagtap becomes blocked the slag will accumulate in the reaction zone and the combustion process must be interrupted to clean the slagtap. Apart from the loss of production involved in stoppage of the process, there is also the aspect of poor accessibility of the reaction zone owing to the high process temperature and pressure, which will result in the cleaning of the slagtap being a complicated and time consuming matter.